1. Field of the Invention
The present invention pertains to the field of ophthalmic wavefront sensing and, particularly, to apparatus and associated methods for aberrometer calibrations.
2. Description of Related Art
A wavefront sensor, often referred to as an aberrometer (which term will be used interchangeably herein), is a device that measures a difference in the optical path of light between a deformed wavefront and an ideal, or reference, wavefront. The measurement, when properly processed, yields values for various aberrations in the optical system that the light propagates through, and which deform the wavefront. Although high-energy lasers and astronomical imaging were primary drivers for wavefront sensor development (where the atmosphere itself was the aberration causing optical system), more recent attention has focused on measuring the aberrations of the eye with the goal of improving visual quality. The interested reader is directed to Geary, J M, Introduction to Wavefront Sensors, SPIE Optical Engineering Press (1995); Williams"" U.S. Pat. No. 5,777,719, for more information. These references, to the extent permitted by applicable patent rules and laws, are herein incorporated by reference in their entirety.
The aforementioned Williams"" patent describes a Shack-Hartmann type wavefront sensing instrument that can be used to measure, among other parameters, higher-order ocular aberrations. Many commercial aberrometers incorporate a microlens (lenslet) array and operate on the Shack-Hartmann principle. Other types of aberrometers include the spatially resolved refractometer based on the Scheiner optometer, those based on the Tscherning principle, Skiascopic systems, scanning systems of the Tracey technology type, raytracing devices, and others. All of these aberrometer types are well known in the ophthalmic wavefront sensing art so that a detailed description of these devices is not necessary to understand the invention. Descriptions of these devices can be found, for example, in J Refractive Surg. 16 (5), September/October 2000.
Ocular wavefront data is increasingly being used to configure ablation algorithms for refractive surgery such as, e.g., PRK, LASIK, and LASEK, and for custom shaping of contact lenses, IOLs, onlays and other vision correcting elements. Successful outcomes to these applications depend upon the validity of the obtained aberration measurement which in turn depends on the correct initial calibration of the aberrometer, and on the correct calibration of the aberrometer when it is used to obtain diagnostic/therapeutic wavefront aberration measurements. Accordingly, the inventor has recognized a need for a method and apparatus that addresses these concerns and others relating to the accuracy and reproducibility of wavefront measurement and aberrometer operation.
An embodiment of the invention is directed to an improved wavefront sensing device. An aberrometer, regardless of its operating principle, requires an optical head, a data acquisition, storage and processing system for detecting, measuring and displaying wavefront aberration data, and interlinking electronics and software. The improvement according to the invention is characterized generally by an aberrometer calibration component located in an optical path of the wavefront sensor, and an archived calibration measurement of the calibration component that accurately represents a desired measurement parameter of the calibration component. The calibration component preferably comprises a well-characterized test optic or model eye. In a preferred aspect of this embodiment for wavefront measurement calibration, the calibration component is a model eye having a known wavefront aberration, and the desired measurement parameter is a Zernike aberration coefficient for making a wavefront measuring calibration. In another aspect relating to aberrometer refractive focusing calibration, the calibration component is a test optic having a known plus or minus dioptric power, and the desired measurement parameter is a refractive calibration or aberrometer focusing calibration. These calibration components may be used exclusively or in combination. One or more controllable light transmitting elements, e.g., shutters or apertures, are disposed in the optical path to selectively transmit light to and from the calibration components such that calibration and diagnostic/therapeutic measurements can be separately obtained. In addition to the calibration component(s), a light intensity or power meter is disposed between the retinal illumination source of the aberrometer and the patient""s eye to provide a safety function against dangerously high (or inadequately low) levels of retinal illumination. Any or all of the aforementioned components can be cooperatively engaged with an interlinking aberrometer processing and control center to prevent diagnostic and/or therapeutic operation of the aberrometer if it is out of calibration or unfit or unsafe for use.
The invention further contemplates associated calibration and monitoring methods of operation.